Perpendicular magnetic recording (PMR) has been developed in part to achieve higher recording density than is realized with longitudinal magnetic recording (LMR) devices and is believed to be the successor of LMR for next generation magnetic data storage products and beyond. A single pole writer combined with a soft magnetic underlayer has the intrinsic advantage of delivering higher write field than LMR heads. A conventional PMR write head as depicted in FIG. 1 typically has a main (write) pole 10 with a small surface area (pole tip) at an air bearing surface (ABS) 5 and a flux return pole (opposing pole) 8 which is magnetically coupled to the write pole through a trailing shield 7 and has a large surface area at the ABS. Magnetic flux in the write pole layer 10 is generated by coils 6 and passes through the pole tip into a magnetic recording media 4 and then back to the write head by entering the flux return pole 8. The write pole concentrates magnetic flux so that the magnetic field at the write pole tip at the ABS is high enough to switch magnetizations in the recording media 4.
To achieve high areal recording density with PMR technology, a key requirement for the PMR writer design is to provide large field magnitude and high field gradient in both down-track and cross-track directions. In practice, these two requirements are often traded off with each other to balance the overall performance. To improve the down-track field gradient, a trailing shield PMR writer design has been widely applied today. In FIG. 2, a view from the ABS plane is shown of a conventional trailing shield PMR writer in which a magnetic write shield 12 is placed above the top edge 10b of the write pole 10 by a certain distance d. The bottom or leading edge 10a of the write pole 10 is so designated because it is at the front of the write pole as it moves in the y or down-track direction. With this design, the down-track gradient is improved at the expense of reducing write field. In the cross-track or x direction, however, there is still a quite large detrimental fringe field (not shown) leading out from the write pole 10.
Referring to FIG. 3, another prior art design is illustrated that was proposed by M. Mallary and described in “One Terabit per Square Inch Perpendicular Recording Conceptual Design”, IEEE, Trans. Magn., Vol. 38, July, 2002. To further improve cross-track field gradient, a full side shield writer structure is used to limit the excessive fringe field onto the adjacent track. For example, the writer in FIG. 2 may be modified by adding one side shield 13 along one side of the write pole 10 and a second side shield 14 along the opposite side of the write pole. The side shields 13, 14 have a thickness t equal to the thickness of the write pole 10. Note that the side shields may have sloped sides that parallel the slope in the write pole sides and maintain a spacing or side gap s therebetween. Depending on the size of side gap s, field magnitude could drop below the minimal performance requirement. In addition, the complexity of the structure also poses a great challenge for wafer processing.
For easy processing, other writer structures have been proposed and include a partial side shield design in FIG. 4 and a leading shield design in FIG. 5. Referring to FIG. 4, the partial shields 15, 16 replace the full side shields in FIG. 3 and have one side coplanar with the top edge 10b of the write pole 10 and spaced a distance d from the trailing shield 12. The side of the partial shields 15, 16 facing the write pole 10 may be a side gap distance s from the write pole as in the full side shield example. However, the thickness p of the partial shields 15, 16 is substantially less than the thickness of the write pole 10. In FIG. 5, there are no side shields but a leading shield 17 is positioned a distance m from the bottom edge 10a of the write pole 10. The thicknesses of the shields 12, 17 and the magnitude of m and d may vary depending on the composition of the shields and the performance requirements.
Unfortunately, none of the prior art structures provide satisfactory control of field magnitude and field gradient in both the down-track and cross-track directions. Therefore, an improved write structure is necessary to achieve the high performance required for advanced devices with narrow track widths and high recording density.
A routine search of the prior art revealed the following references. U.S. Pat. No. 7,068,453 describes a write head with a shield structure wherein a flux return pole is connected to a full side shield by soft magnetic connections. In addition, a trailing shield contacts the side shields on opposite sides of the write pole tip. Similarly, in U.S. Pat. No. 7,070,698, a side and trailing shield structure formed around a pole tip is connected to a return pole layer through magnetic side studs. U.S. Pat. No. 7,002,775 also discloses a head for perpendicular magnetic recording with side shields that are connected to a return pole piece by two studs of ferromagnetic material.
In U.S. Pat. No. 6,842,313, a PMR writer is disclosed with a floating write shield that is spaced apart from the write pole thereby enabling the floating shield to be at a different magnetic potential than the write pole.
U.S. Patent Application Publication 2005/0237665 shows a four sided shield structure for a perpendicular write head in which full side shields are magnetically connected to a leading shield. The side shields contact a trailing shield and have a thickness greater than the write pole tip which may reduce the field magnitude.